TM 1-1520-240-102-3-7bustion camber and the other is at the aft end to ensurecomplete drainage.2-3-29. FADEC Description.714A Each engine is controlled by its own Full AuthorityDigital Electronic control System (FADEC) which pro-vides the following features:a.Automatic start scheduling.b.1 and 2 engine load sharing.c.Power turbine speed governing.d.Transient load anticipation (using rotor speedand collective pitch rates).e.Transient torque smoothing (using N2 rates).f.Contingency power capability to meet aircraft de-mand.g.Acceleration and deceleration control.h.Engine temperature limiting throughout the oper-ating range.i.Surge avoidance.j.Compressor bleed band scheduling..k.Fuel flow limiting.l.Engine fail detection.m. Power assurance test.n.Engine history/fault recording.o.Engine-to-engine communication (via databus).p.Automatic switchover to reversionary backup inthe event of a FADEC primary system failure.The FADEC provides automatic engine start, simulta-neously sequencing ignition, start fuel, and stabilizedoperation at idle. A data link between 1 and 2 engineFADEC systems transmits signals to achieve load sha-ring. It also provides control of N1 speed and NR (N2)output shaft speed to maintain the rotor system at a nearconstant RRPM throughout all flight power demand con-ditions. FADEC provides smooth acceleration and over-temperature protection when ECLs (both together) aremoved from GROUND to FLIGHT. Overtemperatureprotection is provided (through the DECU temperaturelimiting function) by control system thermocouple inter-face at the power turbine inlet. The control systemcompares PTIT temperature signals with reference limitsto calculate and provide appropriate N1 acceleration.During starts, an absolute 816_C limit is set and if ex-ceeded an engine out indication and shutdown will occur.If compressor performance deteriorates for any reason,surge detection automatically allows recovery from com-pressor instability while protecting the engine from dam-age due to overtemperature.The FADEC system consists of:q.The Digital Electronic Control Unit (DECU) in-cludes a primary mode and a reversionary section forbackup (fig. 2-3-7).r.The Hydromechanical Metering Assembly(HMA), includes Hydromechanical Fuel Metering Unit(HMU) and fuel pump unit for all fuel metering to supportboth primary and reversionary fuel metering, a self-con-tained alternator for powering the FADEC electronics, aprimary and revisionary compressor bleed air control,and redundant speed sensing.s.ENG COND panel (fig. 2-3-5).t.FADEC control panel (fig. 2-3-6).u.RPM INC/DEC (Beep) switch THRUST CONTLever.(1)On 714A engine installations, engine beepswitches are only active when in reversionary mode.(2)Each switch is labeled NO. 1 or NO. 2 whichis used to adjust RRPM when in reversionary mode.(3)Operation of the beep switches on the714A in the reversionary mode are the same as for the712 except that each switch operates respective en-gine independently. If only one engine is in reversionarymode, the RRPM will not change, as it is governed by theengine in primary mode.2-3-30. Reversionary System. 714ANOTEAircrew should be alert to the possibility ofabrupt NR and engine power changes whenoperating the FADEC in single or dual engineREV mode (s).The reversionary (backup mode) automatically takescontrol of the engine if the primary mode fails or if se-lected by the operator via the FADEC panel, REV switch.When an engine is operating in reversionary mode,FADEC provides engine and rotor control through N1speed governor, beep control, and thrust pitchcompensator.When both engines are in reversionary mode, RRPM willrequire more pilot attention since proportional rotorspeed governor will not hold speed as accurately as theprimary systems. With large collective changes, the rotorspeed can change up to $3 percent from a nominalsetting.The reversionary system provides the following controlfunctions:a.Automatic start sequencing including over tem-perature protection, but not start abort.b.Pilot controlled start fuel enrichment/derichment,if required, through ECL modulation.c.Ground idle set 55 "5 percent with ECL at GND.